Bass Management: A Controversy

[Seth=L]

Why does everyone one on these forums insist that you use bass management on your receiver, or pre/pro amplifier combinations even if someone has exeptional speakers. Before I get rolling, I do beleive that bass management does have a purpose in many applications, just not all.

Now the first argument for this makes perfect sence, reduced stress on the amplifier. There isn't much to argue about there on that particular grounds. But when someone has some really great speakers and sub, the tight bass of your say 6.5 inch woofers is replaced with a slower bass from a 12 inch woofer.

That especially applies to more powerfull pre/pro amp combos. If you have an amp with more power then you would use, then why set the x-over cut-off to 100 hz. Is it easier, maybe, but does that mean it sounds better?

This is just something that has made me itch for a while and I want your guys' take on this subject.

 

[MDS]

There is a lot more to bass management than relieving stress on the amplifier. First off, which do you think will be better able to reproduce very low frequencies at high SPLs - that 6.5 inch woofer in your 'exceptional' speakers or a subwoofer that is purpose designed to do one and only one thing - reproduce low frequencies? [Allowing for the fact that all subwoofers are not created equal and some are naturally better than others.]

In a multi-channel speaker setup you often have speakers with very different frequency response and power handling abilities. Besides time alignment which makes the sound from different speakers at different locations from the listener arrive at the ears at the same time, bass management routes the frequencies that cannot be handled adequately by the other speakers to a subwoofer which can handle them with relative ease.

Choosing an appropriate xover doesn't really have anything to do with the power of the amplifier. It has everything to do with the frequency response of the speakers and sending them only the frequencies they can reproduce accurately.

 

[Seth=L]

I agree that with home theater applications that bass management is a very helpful tool.

In a 2.1 set-up however, I have a different view. If you have a pair of floorstanding speakers that use two 6.5 inch drivers in a sealed cabinet and a subwoofer with a 12" woofer in a acoustic suspension cabinet. The sub has usefull output down to say 19hz, the sub is designed to go deep and loud. The towers have usefull output down to 60 hz before they start to slowly rolloff. The towers have quick, punchy bass that the subwoofer would have trouble keeping up with, because well designed smaller drivers are usually going to beat a large sub on speed. Setting the X-over to 100 or higher is going to take away some of the lower bass that would have been handled great by the speakers and make is sound more sluggish than it should.

Another thing to consider is how localized the bass becomes as you rise the x-over. I don't want to know it is there when I am listening to my music.

This thread is more directed to music listening than home theater.

 

[MDS]

I thought the intention may have been towards 2.1 rather than HT but the principle remains the same.

The frequency at which bass becomes localizable is up for debate but 60 Hz is definitely not localizable. Dolby released a paper some time ago where they claimed that except in the rarest of circumstances even bass as high as 150 Hz is not localizable. It's no coincidence that 120 Hz was chosen as the top end for the LFE channel because it is geneally not localizable.

The towers have usefull output down to 60 hz before they start to slowly rolloff. The towers have quick, punchy bass that the subwoofer would have trouble keeping up with, because well designed smaller drivers are usually going to beat a large sub on speed.

If 60 Hz is the spec'ed low frequency extension, it is already down 3 dB at that point and will be down a whole lot more at even lower frequencies - how much depends on the slope of the xover of course. The bass won't be 'quick' from the towers; the notion of 'quick' or 'slow' bass is audiophile nonsense. If the woofer isn't 'fast' enough it will be playing a different frequency than what was intended.

Remember that all speakers roll off at a rate determined by the slope of their xover. The goal of setting a xover to the sub is to match the slopes of the low pass from the receiver and the high pass of the speaker so that at the chosen frequency the amplitude change is zero (or as close as possible).

 

[Seth=L]

the notion of 'quick' or 'slow' bass is audiophile nonsense. If the woofer isn't 'fast' enough it will be playing a different frequency than what was intended.

When a driver is fed a signal in moves, and as long as it is still moving it is producing sound. Larger, heavier drivers take longer to stop moving.

 

[MDS]

When a driver is fed a signal in moves, and as long as it is still moving it is producing sound. Larger, heavier drivers take longer to stop moving.

Same as the woofer in the tower speakers. Why do you think that the towers respond perfectly but the sub cannot?

 

[MACCA350]

If you set your Xover, phase and levels correctly you won't even know there is a separate sub in the system, it disappears and you end up with a full range sound. Most people set the sub volume too high and this is why they don't like the sub on for music. If its set properly the sub serves as an extension of your mains and not a BOOST in the low end.

cheers

 

[Seth=L]

Same as the woofer in the tower speakers. Why do you think that the towers respond perfectly but the sub cannot?

I didn't say perfect. I would say that the tower has a better chance of responding quicker dependent on if it is receiving a signal or not. For example, obviously a tweeter responds much faster than a woofer, this is a dramatic comparison of course. But none the less a smaller driver should, and most cases does respond faster than a larger one. This is exactly why they try to design very light weight, rigid dynamic driver cones, to increase the responce time. However a properly integrated servo system could force a large driver to respond more like a small driver.

 

[MDS]

Newton's First Law - Inertia: An object at rest tends to stay at rest; an object in motion tends to stay in motion.

No matter how big or small you cannot repeal the laws of physics. If you think that a woofer in a tower speaker is immune to the laws of physics but a woofer in a subwoofer is not then OK.

By the way, do you know the shortest interval of time at which humans can distinguish a change in sound? It's another area that is open to debate because as usual it depends on a lot of factors but let's just say that it is an order of magnitude or more greater than any delay caused by the inertia of a typical speaker.

 

[Seth=L]

Which is easier to stop moving, a semi tractor and trailor, or a GEO Metro? I am not implying that a small driver defeats the laws of physics and a large one doesn't. Slow, sloppy bass don't just come from crappy cabinet designs, but the drivers themselves.

 

[Seth=L]

By the way, do you know the shortest interval of time at which humans can distinguish a change in sound? It's another area that is open to debate because as usual it depends on a lot of factors but let's just say that it is an order of magnitude or more greater than any delay caused by the inertia of a typical speaker.

Do you? I would certainly like to know myself.

 

[MDS]

On average, 6 ms.

 

[Seth=L]

So you are saying that a driver, any driver, can stop moving after it is no longer receiving a signal in 6 thousandths of a second?

 

[MDS]

So you are saying that a driver, any driver, can stop moving after it is no longer receiving a signal in 6 thousandths of a second?

No, I am saying that the average person cannot hear a change in sound between two tones if that change happens faster than 6 ms. So if your 'slow' driver tries to change from one frequency to another and continues to play the old frequency for less than 6 ms you won't notice anyway.

 

[mtrycrafts]

Larger, heavier drivers take longer to stop moving.

Absolute nonsense.
You better check the output of that 6.5" driver at 60 Hz, how loud you can drive it, or even at 70 Hz.

 

[mtrycrafts]

It has everything to do with the frequency response of the speakers and sending them only the frequencies they can reproduce accurately.

What good is accuracy if you cannot hear the volume level you are trying to send that driver? Just because a driver is moving doesn't mean you will hear it, especially when you hear everything else in a musical passage.

 

[Nick250]

Why does everyone one on these forums insist that you use bass management on your receiver, or pre/pro amplifier combinations even if someone has exeptional speakers. Before I get rolling, I do beleive that bass management does have a purpose in many applications, just not all.

Now the first argument for this makes perfect sence, reduced stress on the amplifier. There isn't much to argue about there on that particular grounds. But when someone has some really great speakers and sub, the tight bass of your say 6.5 inch woofers is replaced with a slower bass from a 12 inch woofer.

I will leave the fast/slow 8 ms tech stuff to MDS and Mtry. My personal experience in the 5 years I have had my Hsu VTF-2 and Paradigm Studio 20's is that I have never felt the Hsu did not keep up with the speakers.

That especially applies to more powerfull pre/pro amp combos. If you have an amp with more power then you would use, then why set the x-over cut-off to 100 hz. Is it easier, maybe, but does that mean it sounds better?

While the THX and de facto industry standard is a 80Hz crossover, I don't think you would get a lot of argument from most folks that the crossover point is a factor of speakers, sub, room acoustics, intended use, and personal preference. I waffle between 60Hz and 80Hz for the fronts for music, and use 80Hz for HT. All the speakers are set to small.

I might add that for music my view is that a well integrated sub does not draw attention to itself. It provides a low frequency foundation and is only noticeable by it's absence.

This is just something that has made me itch for a while and I want your guys' take on this subject.

 

[Seth=L]

Absolute nonsense.
You better check the output of that 6.5" driver at 60 Hz, how loud you can drive it, or even at 70 Hz.

That was a hypothetical speaker system for starters. And second, why is it always about output. I am discussing accuracy, not loudness. A subwoofer is going to produce louder bass than a speaker system in most cases.

Many subwoofers suffer from audible overhang, slowness of bass. If a drum wack sounds more like a lingering dong on a sub and not on some nice full range speakers, then what is causing that?

 

[Seth=L]

I will leave the fast/slow 8 ms tech stuff to MDS and Mtry. My personal experience in the 5 years I have had my Hsu VTF-2 and Paradigm Studio 20's is that I have never felt the Hsu did not keep up with the speakers.

I have also owned the STF-2, and being that it is a 10" it should be more transient. Does it compete with the sheer power of my M&K?, no, but it does a pretty good job. Not all subs do though.

 

[MACCA350]

why is it always about output. I am discussing accuracy, not loudness.

I've seen my towers dual 6.5" woofers pound in and out on a 20Hz tone but there's jack output, now play that 20Hz tone through the DD and it's enough to tear the house down. So you tell me whats more accurate? You need both frequency and amplitude, and 6.5" woofers(in the real world) won't do much below 40Hz(If that and definately not at high volumes).

So If you want accurate reproduction then you need to reach below 20Hz for starters an that means large woofers and lots of power to move lots of air for enough output down low. Some subs are more accurate in transient response than others and this is where design and quality come into play and the reason servo systems were invented.

Just remember that your room itself plays a huge role in the accuracy of your sound especially in the low end.

cheers